Apparatus for determining dew point of gases



Feb. 15 1938. I A. B. MARTIN ET AL APPARATUS FOR DETERMINING DEW POINTOF GASES Filed NOV. 28, 1936 TOE ENTORS A RNEY ARMOR B. MARTIN HENR NWADE Patented Feb. 15, 1938 UNITED STATES 2,108,173 APPARATUS FORDETERMINING DEW POINT OF GASES Armor B. Martin. Butte, Mont., and HenryN. Wade, Los Andes, Calif.

Application November-.28, 1936, Serial No. 113,210

- 4 Claims.

' The object of our invention is to provide a means for rapidly andaccurately determining the temperature at which a sample of gas becomessupersaturated with water vapor and begins to separate liquid water.

It is well known to determine the dewpoint of a gas byv bringing it intocontact with a polished and chilled metal surface and observing thetemperature at which the surface is dimmed by the collection of water'drops thereon. This method is far from satisfactory: first becauseincipient dew formation is difiicult to observe and because thetemperature at which dew forms is influenced by the temperaturedifferential between the plate which it may be maintained at pipe linepressure,

at least a portion of the surface contacting the gas being highlypolished; second in applying a slow chilling effect to the tube by whichits temperature is gradually lowered; third, in directing a light beamagainst the polished portion of the tube, from which it is reflected toan eyepiece, this beam being extinguished by diffusion as soon as thepolished and chilled reflecting surface becomes covered with even themost minute drops of condensed water.

By this method, and in apparatus hereinafter described, determinationsof dewpoint may be made with extreme accuracy, in a minimum of time, andunder any pressure within the limits fixed by the structure of theapparatus.

It will be evident that this general type of apparatus may be givennumerous modifications, but it will suifice to illustrate two of thesein the attached drawing and the appended description thereof, in whichFig. 1 illustrates in vertical section an apparatus 4 in which thereflecting surface is formed'on the exterior of a tube containing thechilling agent and the sample of gas is retained within a surroundingshell;

Fig, 2 illustrates in the same manner an apparatus in which thereflecting surface isformed on the interior of a tube through which thegas sample is passed and the chilling agent is retained in thesurrounding shell,'and

Fig. 3 illustrates a light-mask which may ,used with the apparatus ofFig. 1.

and the gas, both tending to give unduly low readlighted and, the imageReferring first to Fig. l, I!) is a cup-shaped container having a cap Il which is detachable for cleaning and is firmly bolted down. Thiscontainer mustbe capable of withstanding the highestpressure at whichthe dewpoint of a-gas is to 5 be determined. Projected downwardly fromthe head is an inner tube l2 having its lower end closed and being ofsuch thickness as to withstand the external pressure of the gas. Thistube, which should be of a hard and noncorrosible 10 metal, is flattenedand highly. polished at one side for a portion of its length, as at I3,theremaining external surface being protected by heat insulation l4.

The inner tube i2 is open at its upper end but 16 should be providedwith a cap l5 having an opening l6 for the introduction of the chillingliquid and the escape of vapor therefrom, and with a gland I1 throughwhich a thermometer I8 may be inserted into this liquid.

The outer container has a pipe-threaded inlet opening l9 and a similaroutlet opening 20. These openings would ordinarily be provided withcontrol valves, not shown. Inside the outer container is placed a mirror25 2| arranged in parallel to the flattened reflecting face [3; Foradjustment of position this mirror may be provided with a three-pointsupport consisting of the pin 22 and a pair of adjusting screws 23bearing against the lower corners (only one 30 of these screws beingshown) and may beheld against these supports by a spring, as for examplethe expanding ring 24.

Openings 25 and 26 are formed in the wall of' the container, bothoftheseopenings being di- 35 rected toward ends of the reflectingsurface Hi. The openings are closed by thick glass discs ll and 28retained by glands 29 and 30, a ring of soft packing being placed oneach side of each disc. Finally, a smallelectric lamp 3! is sup- 40ported in any convenient manner in the axis of opening 25. 1

The functioning 0 this apparatus is as follows: The container is flll'edwith the gas to be tested, under the desired pressure, and preferably avery 5 slow stream of the gas is allowed to flow through it. The innertube I2 is filled with a volatile liquid boiling below the dewpoint ofthe gas, as for example a mixturev of propane and butane. This mixturecools itself by vaporization at atmospheric pressure and, if the coolingeffect is produced too rapidly, a vent valvemay be placed in opening l6by which vaporization may be retarded to any desired-extent. The lamp isnow,

of opening 25. a spot of light, becomes visible at point ll at the endof opening 24, being reflected from the polished surface I! to themirror surface ii and vice versa along the path of the dotted line33-43. It will be understood that this repeated reflection merelyincreases the sensitivity of the instrument and that the openings may beso arranged that the light beam is directed against surface l3 anddirectly reflected to point 32 at which it is ob-' served, the mirror itthen being unnecessary.

1 As the temperature of the volatile liquid within the tube I! islowered by vaporization, the tem- Derature of the polished surface I 3is simultaneously reduced, the transfer of heat from this surface beingrendered very rapid by the ebullition of the liquid within the tube.When a temperature is reached at which the him of gas in immediatecontact with'the polished surface becomes supersaturated, this surfaceis clouded by the collection of multitudinous minute drops of water, thelight beam passing through opening is diffused, and the image formerlyvisible through eyepiece l2 disappears. At this point the .temperatureis read on thermometer |8,'this temperature being-the dewpoint of thegas at the pressure carried in the shell.

Referring now to Fig. 2, 40 is a cylinder provided with caps 4| and 42to form a liquid tight shell. A second shell 43 provided with a venttube 44 is connected at both ends with shell 40 as -by tubes 45 and 4'.Into thelower tube is passed a small tube 41 terminating in a minutevent for the introduction of a stream of air or gas under pressure toproduce circulation of a cooling liquid through the twoshells.

The upper cap 42 is provided with an opening and a gland 48 for theinsertion of a thermometer 49. It is also provided with a well 80tightly capped as at II, this well having a vent II which may beprovided with a control valve not shown.

From the bottom of this well a copper tube l3 passes to a similar well54 formed in lower cap 4|. This tube is rolled or beaded into the capsto form a gas-tight joint adapted to withstand pipeline pressures. Thelower well has a closure plug 54 and an inlet opening 55 f)!- the gas tobe The copper tube 43 is' wound into a long helix or other form whichwill prevent any direct rays of light from a lamp 46 from reaching themirror 51 placed in the lower well. If the helix be not too sharplycurved, however, the mirror will reflect into the eyepiece 88,

fixed in the wall of the lower well, a red glow or spot of red lightproduced by repeated reflections of rays from the lamp against thepolished inner wall of the tube.

When a slow stream of the gas to be tested is passed upwardly throughtube 53, the two shells being filled with a volatile liquid as describedand a circulation of this liquid induced by a stream of air or gas, thewall of the tube is cooled to the temperature of the liquid, and as thistemperature is lowered by evaporation of the liquid,-it will reach apoint at which the gas becomes supersaturated and begins to deposit dewon the placed in the upper wellv ture of said wall, and change in theintensity of said repeatedly reflected inner surface of the gas tube. Atthis point the internal reflection is destroyed by diffusion of thelight rays and the red spot formerly visible in the eyepiece disappears.

The sensitivity of the instrument illustrated in Fig. 1 may be increasedby placing next to the glass disc 21 an opaque mask having a perforationof some definite form, as for instance the mask illustrated in Fig. 3 inwhich the outer portion 50 is opaque while the figure is transparent.This flgure or any other having a definite outline is less likely toconfuse the eye than a round spot such as'corresponds to the unmaskedopening, particularly as in this form there is always a certain amountof diffused light so that the spot does not completely disappear at thedewpoint but only becomes dimmed. The broken flgure corresponding to theopening in the mask does, however, disappear almost completely, mergingin the faintly illuminated ground, giving a sharp indication of thedewpoint.

We claim as our invention:

1. Apparatus for determining the dewpoint of a gas, comprising: a heatconductive wall having a permanent light reflecting surface formedthereon; means for excluding diffused light from said reflectingsurface; means for projecting a light beam onto said surface and forvisually observing the reflection therefrom; means for contacting saidgas with said reflecting surface; means for progressively cooling saidwall, and means for determining the momentary temperature of said wall.I

2. Apparatus for determining the dewpoint of a gas, comprising: a lightsoifl'ce; a metallic tube internally polished and bent to interruptdirect light rays from said source and to transmit reflected light;means for passing said gas through said tube; means for progressivelycooling said tube; means for visually observing said reflected light,and means for determining the momentary temperature of said tube.

3. Apparatus for determining the dewpoint of a gas, comprising: a vesseladapted to contain-said gas: a permanent light reflecting surface ar--ranged within said vessel; means for excluding diffused light from saidsurface; means for progressively. cooling said reflecting surface; meansfor determining the momentary temperature of said reflecting surface;means for projecting a light beam against said reflecting surface, and

' means for observingvthe reflected light beam.

4. Apparatus for determining the dewpoint of a gas, comprising: aheat-conductive wall having a permanent light reflecting surface formedthereon; means for projecting alight beam onto said surface: means forcausing said light beam to be repeatedly reflected from said surface;means for contacting said gas with said reflecting surface; means forprogressively cooling said wall; means for determining the momentarytemperameans for observing a light beam.

. ARMOR B. MARTIN.

HENRY N. WADE.

